1. Field of the Invention
The present invention relates to an image processing apparatus and an image processing method. More particularly, in a system comprising an image processing apparatus, e.g., a personal computer, and a printing device, e.g., a printer, the present invention relates to a process of previewing a copy-forgery-inhibited pattern image that is used to clearly distinguish a copy and an original from each other.
2. Description of the Related Art
Hitherto, sheets of paper including special prints made on them, called forgery-inhibited sheets, have been used for the purpose of prohibiting or inhibiting copying of specific sheets, resident cards and so on. The forgery-inhibited sheet prints on it a string of characters, e.g., “COPY”, in such a way that the characters are hard to visually recognize in an original sheet, but they appear on a copied sheet when the original sheet is copied by a copier or the like. This enables a print sheet, as an original, to be easily visually discerned from a copy obtained by copying the original. The use of those forgery-inhibited sheets is effective in promoting hesitation about using of the copies. Also, there is a psychological checking effect of inhibiting an action of copying itself. The reason why a string of characters are made hard to visually recognize on an original forgery-inhibited sheet resides in enabling an original and a copy to be clearly distinguished from each other. If a character string, e.g., “COPY”, is clearly visually discernable on the original, the original would be possibly recognized as a copy, and the effectiveness of forgery-inhibited sheets would be lost.
Wicker (U.S. Pat. No. 5,788,285) and Mowry et al. (U.S. Pat. No. 6,000,728) disclose techniques for use in producing the forgery-inhibited sheets.
However, because the forgery-inhibited sheets are produced by using special printing techniques, the sheet cost is higher than ordinary sheets. Another problem is that it is only possible to make only characters or the like appear after copying, which were set in production of the forgery-inhibited sheets. Accordingly, the range in use of the forgery-inhibited sheets and a character string set for printing on them is restricted. Stated another way, known forgery-inhibited sheets are poor in flexibility in use due to restrictions in production of the sheets.
On the other hand, with the progress of conversion of various contents into digital data, contents of specific sheets, resident cards, etc. are also converted into digital data. However, the digitization in handling of the digital data, i.e., in utilization of specific sheets, resident cards, etc., still remains in a transient stage. In practical use, therefore, contents of digital data prepared using computers are output onto sheets by, e.g., a printer in many cases.
Under such situations, due to recent drastic development of printer performance, attention is paid to the on-demand printing technique that employs a computer and a printer to print sheets having a similar effect to that of known forgery-inhibited sheets. Japanese Patent Laid-Open Nos. 2001-197297 and 2001-238075 disclose techniques for outputting an image, called a copy-forgery-inhibited pattern in a background of the contents data in superimposed relation when contents data prepared using a computer is output for printing by a printer. On an original (printed output from the printer), the copy-forgery-inhibited pattern image looks like a mere pattern or background when viewed by human eyes, but appears on a copy as predetermined characters, for example, when the original is copied. As a result, a similar checking effect to that of the forgery-inhibited sheets can be developed to check persons trying to copy the original.
When outputting a copy-forgery-inhibited pattern image prepared using a computer in superimposed relation, ordinary print sheets or the like are usable. Therefore, the cost performance is higher than the case using the forgery-inhibited sheets. Furthermore, the copy-forgery-inhibited pattern image can be formed at the same time as printing the contents. This feature realizes free setting of characters, etc. to be visualized when the original is copied. Still another advantage is that dynamic information, such as the name of a user having executed the printing and the output date, can also be allowed to appear as a string of characters.
As described above, when an original is copied, the copy-forgery-inhibited pattern is intended to visualize predetermined characters that were not discernable before the copying, in a copy, and to provide the effects of inhibiting the use of the copy and enabling the relevant sheet to be easily visually recognized as not an original, but a copy. To develop those effects, the copy-forgery-inhibited pattern image basically comprises two areas: (1) an area where, after copying, an image remains (appears) on a copy, and (2) an area where an image disappears on a copy or its density is reduced as compared with the image of the former area to such an extent that the image in the latter area is hard to recognize. These two areas have substantially the same density in the state as it is after printing. Looking at a print (original) from the macroscopic viewpoint, an observer cannot recognize that a character string, e.g., “COPY”, to be visualized upon copying is concealed (buried). Looking it from the microscopic viewpoint, i.e., from a level of print dots, however, the two areas have different characteristics as described below.
For convenience of description, an image appearing after copying is referred to as a “latent image” hereinafter and an image disappearing or becoming paler after copying is referred to as a “background image” hereinafter. The copy-forgery-inhibited pattern image basically comprises the latent image and the background image. In some cases, the copy-forgery-inhibited pattern image further includes a camouflage image. The latent image is sometimes called a foreground image.
Copy-forgery-inhibited pattern printing is not limited to the above-described case, and is applicable so long as a character string (e.g., “COPY”), a logo, a pattern or the like appears (or is visualized) on a copy in a form recognizable by human eyes. In other words, the intent of the copy-forgery-inhibited pattern printing is achieved even when the character string, e.g., “COPY”, appears on a copy in the form of hollow-space characters. In this case, the character string of “COPY” is formed as a background image.
In an electrophotographic or ink-jet dot printer, the area where an image remains on a copy (i.e., the latent-image area or the foreground-image area) is constituted by a set of concentrated dot masses. Also, the area where an image disappears on a copy or an image is reproduced at a lower density than that in the area where an image remains (i.e., the background-image area) is constituted by a set of distributed dots. Further, in the state of the copy-forgery-inhibited pattern image being printed, those two areas are formed substantially at the same density so that the density of the entire copy-forgery-inhibited pattern image is almost uniform.
FIG. 27 shows those two areas. As shown in FIG. 27, the copy-forgery-inhibited pattern image comprises the background-image area where dots are distributed and the latent-image area where dots are concentrated into masses. These two areas can be produced by using different types of halftone dot processes or different types of dither processes.
When a copy-forgery-inhibited pattern image is produced by the halftone dot process, the halftone dot process using a small number of lines is suitable for the latent-image area, and the halftone dot process using a large number of lines is suitable for the background-image area. When a copy-forgery-inhibited pattern image is produced by the dither process, the dither process using a dot-concentrated-type dither matrix is suitable for the latent-image area, and the dither process using a dot-distributed-type dither matrix is suitable for the background-image area.
Generally, a copier has a limit point in the reproducing performance that depends on an input resolution in reading minute dots of a document and an output resolution in reproducing the minute dots. When dots in the background-image area of the copy-forgery-inhibited pattern image are formed in a size smaller than the limit-point size at which dots are reproducible by the copier and dot masses in the latent-image area are formed in a size larger than the limit-point size, an image of large dot masses in the copy-forgery-inhibited pattern image is reproduced on a copy and upon copying, an image of small dots is not reproduced on the copy. As a result, a latent image is visualized on the copy. Even when the distributed small dots do not completely disappear after copying and form the image at a lower density after the copying than the image formed by the concentrated dot masses, the latent image can be noticeably recognized in a relative sense.
FIGS. 28A and 28B show visualization of a latent image. FIG. 28A represents a state that a copy-forgery-inhibited pattern image has been printed. FIG. 28B represents a copy obtained by copying a printed sheet of FIG. 28A by a copier. As seen in FIGS. 28A and 28B, after the copying, a latent image formed by a set of concentrated dot masses appears, but a background image formed by distributed dots disappears.
It is well known that the so-called “camouflage” technique is also applied to the process of forming a copy-forgery-inhibited pattern image for making it harder to recognize the presence of a latent image buried in an original. As used herein, “camouflage” refers to a technique for arranging a pattern with a density different from those of the latent-image area and the background-image area in an overlap relation to the copy-forgery-inhibited pattern image. In the copy-forgery-inhibited pattern image formed using the camouflage technique, a camouflage image with a density different from those of the latent-image area and the background-image area is more conspicuous in the original, while the latent image is less correspondingly noticeable in the original. The camouflage image has another effect of giving an additional aesthetic impression to a print.
FIG. 29A shows a copy-forgery-inhibited pattern image without a camouflage image. FIG. 29B shows a copy-forgery-inhibited pattern image with a camouflage image. When forming a camouflage image, dots constituting the camouflage image are desirably not reproduced on a copy so that a latent image visualized on the copy upon copying can be easily recognized. This point can be realized by forming the camouflage image as a hollow-space image, for example, as shown in FIG. 29B.
In printing of data, such as a document or an image, by a printing device, e.g., a printer, the print preview function is known to display an image, which is to be printed, on a screen for presentation to a user before actually printing the data on a sheet. With the print preview function, the user is able to check the printed image and to confirm a desired layout, etc. When data is printed along with a copy-forgery-inhibited pattern image, it is conceivable to similarly confirm based on the print preview function whether the copy-forgery-inhibited pattern image is correctly added to contents of a sheet that is to be output for printing.
In the print preview function, however, because the image to be output for printing is displayed on a screen of a display device, the print image is generally displayed in a size smaller than that actually printed on a print medium, such as a sheet of paper. This leads to difficulty in recognizing the preview display of the copy-forgery-inhibited pattern image. One reason causing such a difficulty is that the copy-forgery-inhibited pattern image is itself displayed in a small size. Further, for scaling-down of an image, the image is processed by a method accompanied with a partial loss of image information, such as data thinning-out. Therefore, another problem is that even when the copy-forgery-inhibited pattern image or a latent image and a background image thereof are separately displayed, it is not easy to visually confirm the images. In other words, because the copy-forgery-inhibited pattern image, i.e., the latent image and the background image (including a camouflage image as required), are inherently formed to make it harder to distinguish the latent image and the background image from each other, a difficulty in visually confirming the images with preview display may increases. These problems are described in more detail below.
Generally, the resolution of a display device is lower than the resolution of a printer or the reproduction resolution of a copier. Also, with the print preview function, the image to be printed is displayed on a screen of the display device in a smaller sheet display area, and the print image displayed in that smaller area has a lower resolution. For that reason, the copy-forgery-inhibited pattern image is displayed through a scaling-down process. This leads to the following problems. First, the background image formed by high-density minute dots and the latent image formed by low-density dot masses often have respective densities different from their original ones. Second, respective contours of the latent image and the background image are often deformed to some extent.
Known algorithms for the scaling-down process are based on simple thinning-out of pixels, the logical sum of nearby dots, the logical product of nearby dots, etc. FIG. 30 shows examples in which a copy-forgery-inhibited pattern (dot data) 3701 is scaled down to a ½ size in accordance with each of those three algorithms. A pattern 3702 shows a step in the course of scaling-down by the simple thinning-out. With this algorithm, in the case of ½ scaling-down, the original pattern 3701 is divided in units of a 2×2 small area, and a scaled-down image is formed by collecting only an upper left dot in each small area. A pattern 3703 represents a copy-forgery-inhibited pattern resulting after the ½ scaling-down by the simple thinning-out of dots.
A pattern 3704 shows a step in the course of scaling-down by the logical sum and the logical product of nearby dots. As with the simple thinning-out, in the case of ½ scaling-down, the original pattern 3701 is divided in units of a 2×2 small area surrounded by thick lines. Then, the logical sum or the logical product is computed for dots in each small area, thereby successively deciding each dot after scaling-down. The illustrated example represents the case in which the logical operation is executed based on the RGB expression. A pattern 3705 represents the result obtained after the ½ scaling-down of the pattern 3701 by the logical product algorithm, and a pattern 3706 represents the result obtained after the ½ scaling-down of the pattern 3701 by the logical sum algorithm.
As is apparent from those scaling-down results, the obtained patterns differ from the original pattern 3701 at a microscopic level corresponding to a dot array. Also, with the scaling-down based on the logical sum and logical product of nearby dots, the number of white or black areas is increased. Particularly, discrete dots as a feature of the copy-forgery-inhibited pattern are all lost with the scaling-down based on the logical product. Further, in the case of the simple thinning-out, large dots and small dots distinguishable from each other in the original copy-forgery-inhibited pattern 3701 are no longer distinguishable.
Stated another way, a change of the pattern and a change of the dot density at a microscopic level appear at a macroscopic level, at which the user views the image displayed on the display device, such that respective contours of the latent image and the background image are deformed and respective densities of both the images are changed.
Thus, when the copy-forgery-inhibited pattern image or the latent image and the background image thereof are displayed on a previewer as they are, it is difficult for the user to confirm whether printing is performed with a proper process of the copy-forgery-inhibited pattern.
Even when the display device has a high resolution and an image is displayed by simple scaling-down without the pixel reducing process, such as thinning-out, there is a problem. Specifically, because of the display area having a small size in itself, when the copy-forgery-inhibited pattern image or the latent image and the background image thereof are displayed on a previewer as they are, it is not easy to visually confirm those images that are inherently hard to discern.